1. Field of the Invention
The present invention relates to a process for making an electronic chip device having a plurality of elements on one insulating chip substrate such as a multi-element chip resistor device having two or more film resistors.
2. Description of the Related Art
A conventional multi-element chip resistor device incorporating two or more film resistors has such a structure as shown in FIGS. 1 and 2.
Specifically, an insulating chip substrate 1 made of a ceramic material has an upper surface formed with a plurality (two in the figure) of film resistors 2, terminal electrodes 3 at both ends of each film resistor 2, and a cover coat 4 covering the film resistors 2. On the other hand, side electrodes 5 are formed on both side faces 1a, 1b of the insulating substrate 1 in electrical connection to the terminal electrodes 3. Further, grooves 6 are provided respectively on the side faces 1a, 1b of the insulating substrate 1 at a position between the side electrodes 5 in order to provide a complete electrical separation between the side electrodes 6 (see JP-A-6-99567, for example).
Conventionally, in manufacturing a multi-element chip resistor device having such a structure, a ceramic material plate A is first prepared which corresponds to a multiplicity of insulating substrates 1, as shown in FIG. 3. The ceramic material plate A is provided with a plurality of lengthwise break grooves A1 and a plurality of widthwise brake grooves A2 for division of the ceramic material substrate A into individual insulating substrates 1. In addition, through-holes A3 are formed in the ceramic material plate A at portions arranged on the lengthwise break grooves A1 and corresponding to the grooves 6 of the insulating substrates 1.
Then, as shown in FIG. 4, the region of each insulating substrate 1 on the surface of the ceramic material plate A is formed with a plurality of film resistors 2, terminal electrodes 3 at both ends of the film resistors 2 and a cover coat 4 covering the film resistors 2 by screen-printing a material paste followed by baking.
Then, the ceramic material substrate A is divided along the lengthwise break grooves A1 into a plurality of ceramic bars Axe2x80x2 (primary division), as shown in FIG. 5. Thereafter, side electrodes 5 are formed on respective lengthwise side faces of the ceramic bar Axe2x80x2 by applying a material paste followed by baking.
Finally, each ceramic bar Axe2x80x2 is divided along the widthwise break grooves A2 into individual insulating substrates 1 (secondary division).
The ceramic material plate A is prepared by forming a plurality of through-holes A3 in a green sheet and thereafter baking it at high temperature.
Due to the high temperature baking, the entire ceramic material plate A deforms in a plane in a manner such that the spacing between the break grooves A1, A2 increases or decreases. However, the variations of expansion or contraction in a plane increases due to the presence of the many through-holes A3.
For this reason, conventionally, multiple kinds of screen masks are prepared in advance in anticipation for different degrees of deformation in screen-printing a plurality of film resistors 2, terminal electrodes 3 and cover coats 4 on the insulating substrates 1 of the ceramic material plate A. One of the screen masks is selected depending on the extent of deformation caused at the time of baking at high temperature.
Accordingly, there is a cost increase problem in forming the film resistors, terminal electrodes and cover coats by screen printing.
In addition, when dividing the ceramic material plate A along the lengthwise break grooves A1 into separate ceramic bars Axe2x80x2 (primary division) after the baking, each ceramic bar Axe2x80x2 may frequently break at the through-holes A3 located at intermediate positions lengthwise of the ceramic bar. This also invites a cost increase problem due to increased occurrence of defective products and hence decrease of yield.
Further, each ceramic bar Axe2x80x2 divided (primary division) from the ceramic material plate A has grooves 6 due to the though-holes A3 in the lengthwise side faces. Accordingly, the ceramic bar may also break intermediately at the grooves 6 at the time of forming the side electrodes 5 on the lengthwise side faces.
Furthermore, when applying a material paste to form the side electrodes 5 onto the lengthwise side faces of each ceramic bar Axe2x80x2, the material paste flows in the grooves 6 to cause electrical conduction between the adjacent side electrodes 5. In other words, the step of forming the side electrodes 5 is also a cause for defective products and hence a low yield, thus further increasing the manufacturing cost.
It is an object of the present invention to provide a manufacturing process which eliminates these problems.
According to a first aspect of the present invention, a process for making an electronic chip device having a plurality of elements is provided which comprises a step of forming at least two elements, terminal electrodes at both ends of each element and a cover coat covering the elements in an area of each insulating substrate on a surface of a ceramic material plate corresponding to a-multiplicity of insulating substrates each of which provides one electronic component; a step of performing primary division of the ceramic material plate into ceramic bars each corresponding to a row of plural insulating substrates; a step of forming grooves in lengthwise side faces of each ceramic bar between the terminal electrodes; a step of forming side electrodes on the lengthwise side faces of the ceramic bar; and a step of performing secondary division of the ceramic bar into individual insulating substrates.
In this manner, since the ceramic material plate is primarily divided into ceramic bars and grooves thereafter are formed on both lengthwise side faces of each ceramic bar, there is no need to form through-holes in the ceramic material plate for forming grooves on both side faces of each insulating substrate. In other words, the ceramic material plate can be baked without forming a multiplicity of through-holes, making it possible to reduce variations or unevenness of deformation in a plane caused upon baking the ceramic material plate. It is thus possible to reduce the cost required for forming elements such as film resistors, terminal electrodes and cover coats by screen-printing, as compared with the conventional process.
In addition, the ceramic material plate is free of through-holes required in the conventional process for forming grooves. Accordingly, when performing primary division of the ceramic material plate into ceramic bars, it is possible to reduce the likelihood that each ceramic bar breaks at intermediate positions, thereby reducing the number of defective products for improving the yield. Thus, combined with a cost reduction for the above-described screen-printing, the manufacturing cost can be greatly reduced.
According to a second aspect of the invention, a process is provided for making an electronic chip device having a plurality of elements, the process comprising a step of forming at least two elements, terminal electrodes at both ends of each element and a cover coat covering the elements in an area of each insulating substrate on a surface of a ceramic material plate corresponding to a multiplicity of insulating substrates each of which provides one electronic component; a step of performing primary division of the ceramic material plate into ceramic bars each corresponding to a row of plural insulating substrates; a step of forming side electrodes on lengthwise side faces of each ceramic bar; a step of forming grooves in the lengthwise side faces of the ceramic bar between the terminal electrodes; and a step of performing secondary division of the ceramic bar into individual insulating substrates.
In this manner, grooves are formed in each ceramic bar after forming the side electrodes on the ceramic bar. Accordingly, in the step of forming the side electrodes on the ceramic bar, the ceramic bar is less likely to break at intermediate positions. Further, the side electrodes of different film resistors are prevented from electrically conducting with each other via the groove, as opposed to the conventional process. In other words, when forming the side electrodes, it is possible to reduce the number of defective products for improving the yield, thus further reducing the manufacturing cost.
Further, according to a third aspect of the invention, the formation of the grooves in the lengthwise side faces of each ceramic bar is performed with a plurality of ceramic bars laminated one over another, or a plurality of grooves are formed simultaneously with respect to one lengthwise side face of the ceramic bar, or in a manner such that a plurality of grooves are formed simultaneously with respect to both lengthwise side faces of the ceramic bar.
This feature is advantageous in that a plurality of grooves are formed at a time for additionally reducing the manufacturing cost by reducing the time needed for forming the grooves.
In addition, according to a fourth aspect of the invention, the process according to any one of the foregoing aspects of the invention is applicable to the manufacture of a resistor device formed with at least two film resistors on one insulating substrate.
Other objects, features and advantages of the present invention will become apparent from the following description of the embodiments given with reference to the accompanying drawings.